ok, i'm not quite sure what the place i'm in is called but it's in the sewers below the temple dist. I went through a hidden door right when I walked in. It took me down a very short hallway with steps at the end. a caption popped up and said "something very powerful is here". Anyway, i went up down the stairs and into this purple colored room. Opened a door to the left and into a circular room with mind flayers, archers, clerics, & Umber hulks. I killed them all. then went to the next room...i've just opened another door and 4-5 mind flayers come out. I can't seem to kill them or hurt them very much. What does it take? Also, what else will i run into from here?

You should be able to kill them with any magical weapon, I like to use ranged weapons so they can't get too close to intelligence drain. Try casting chaotic commands (priest spell) on whoever your fighters are which will stop them being stunned, and also try drawing them out one by one if you can. There are only mind flayers here, no more nasty surprises

I've found that luring them out one at a time works best. Send someone who's hasted in and lure one of them out, then shut the door behind him and attack with everything you have. Melf Minute Meteors works well also

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Logic is a variable dependant on ones own perception of that which is around them

Been a while since I've had to repost my mindflayer slaying tactics... Here goes....

1. Cast the priest spell Chaotic Commands on your 1 or 2 best fighters. (One casting of CC can get a fighter thru an entire Mindflayer dungeon.)

Have those 1 or 2 fighters drink a potion of Genius or Mind Focusing. This increases your INT and is a cheap armor against mindflayer INT drains. And keep those potions in your quick slots. During the melee, you might need to drink more. You'll more likely die from going negative INT rather than negative HP.

The Shield of Harmony or 2H sword Lilarcor are very useful, as well.

2. If your mage is high enough level, cast a Mordenkain's Sword. It's PERFECT for midflayers. It cannot be affected by psionics. Otherwise/additionally, cast "animate dead" to get some skeletal support. They also cannot be affected by psionics, but the umber Hulks will make short work of them.

3. REGARDLESS ... send the Morden's Sword or the skeletons thru the door first. All mindflayers will focus their initial psi attacks on them and gnore your fighters. After the first wave of psi attacks, send in your fighters and focus your attacks on the mindflayers (i.e. ignore the umber hulks).

You can sneak your other party members up a bit to provide long range support. A Chaos spell can sometimes be useful.

If one of your melee fighters begins taking INT drain damage, suck down another potion to increase their INT. Otherwise, pull that INT drained fighter back to let the INT drain wear off. Let the other fighter take the brunt of the fighting.

During the melee, kill each mindflayer as quickly as possible.

Mindflayers, while very dangerous, are completely manageable when you use the proper tactics.

Chaotic Command is a must spell when facing Mind Flayers. if you have someone with at least 3 attacks/round cast it on them, add Improved Haste and that character should be able to slice through the Mind Flayer lair.
as for Umber Hulks, if you're having trouble hitting them, remember that they die horribly to Death Spell.